xml-rpc problem

I have to talk to a XML-RPC server. I am working within an 
environment that does not support XML-RPC (Cache from Intersystems). 
So the idea was that I write my code directly to HTTP. Now I have 
something but I do not receive a correct reply from the server. They 
say my XML-RPC request is not correct, however they cannot tell me 
what is wrong.
Below is what I send. Could you say what is wrong with this?
(I changed the password.)

Regards,
Pieter van Lierop
Infor Development.

+++++++++++++++++++++++++++++++++++++++++++++++++

POST /adresxpress/server/adresxpress_server.php HTTP/1.0
Connection: Close
Host: www.dataonline.nl
User-Agent: Mozilla/4.0 (compatible; Cache;)
Content-Length: 459
Content-Type: text/xml; charset=UTF-8
 
<?xml version="1.0"?
><methodCall><methodName>adresxpress.postcode</methodName><p
arams><param><value><struct><member><name>username</name><value><stri
ng>oba_01</
string></value></member><member><name>password</name><value><string>X
XXX</st
ring></value></member><member><name>postcode</name><value><string>107
5 KJ</strin
g></value></member><member><name>huisnummer</name><value><string>4</s
tring></val
ue></member></struct></value></param></params></methodCall>




 
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